user
Write a response that appropriately completes the request.

### Instruction:
Describe a function of the immune system.

### Response:
assistant
The immune system is the body's defense system against infection and disease. It is composed of a network of cells, tissues, and organs that work together to identify and eliminate foreign substances, such as bacteria and viruses, from the body. It also helps to destroy abnormal cells that have the potential to become cancerous.